Process for printing leather

ABSTRACT

THE INVENTION RELATES TO A PROCESS FOR PRINTING NATURAL OR SYNTHETIC LEATHER, WHEREIN THE SURFACE TO BE PRINTED IS BROUGHT INTO CONTACT WITH A TEMPORATY CARRIER OF PAPER, ALUMINUM OR REGENERATED CELLULOSE, COMPRISING A TRANSFERABLE FILM OF VINYL RESIN AND ONE OR MORE PIGMENTS, AND AN UNDERLYING LAYER OF ETHYL CELLULOSE, OR OF A MIXTURE OF NITROCELLULOSE AND AN AMINOPLAST, AND THAT THE TEMPORARY CARRIER IS SEPARATED FROM THE ULTIMATE CARRIER.

United States Patent C 3,794,544 PROCESS FOR PRINTING LEATHER Peter Eckert, Magden, Willi Egli, Reinach, Basel-Laud,

and Hans Georg Osolin, Oberwil, Basel-Land, Switzerland, assignors to Ciba-Geigy AG, Basel, Switzerland No Drawing. Filed Feb. 10, 1971, Ser. No. 114,399 Claims priority, application Switzerland, Feb. 18, 1970, 2,329/70 Int. Cl. B44c 1/24 US. Cl. 156-230 14 Claims ABSTRACT OF THE DISCLOSURE Direct printing of leather is rarely carried out in industry, because printing machines generally cannot be employed economically and because a continuous procedure for printing the leather hides, which are irregular in shape and thickness, is not possible.

The present invention is based on the observation that leather can advantageously be printed it the surface to be printed is brought into contact, preferably with the use of heat and/or pressure, with a temporary carrier of paper, aluminum or regenerated cellulose, which comprises a transferable film of vinyl resin and one or more pigments and an underlying layer of ethylcellulose, or of a mixture of nitrocellulose and an aminoplast, the system is cooled if required, and the temporary carrier is separated from the ultimate carrier.

The process is suitable for all natural and synthetic varieties of leather, except those that are heavily greased or otherwise provided with a hydrophobic impregnation.

By synthetic varieties of leather there may be understood leather substitutes or poromerics, for example, Corfam, developed by Messrs. Du Pont (USA). Other similar products are Clarino (manufactured by Kurashiki Rayon Co., Japan), Ortix (manufactured by ICI, England), Hi-Telac (manufactured by Toyo Rayon Co., Japan), Aztran (manufactured by B. F. Goodrich, U.S.A.), Quox (manufactured by Courtaulds, England), Rucaire (Occidental Petroleums Hooker Chemical), Corfam H" (Du Font) and Dorzan (Du Pont). Such poromerics are accurately described in the relevant technical literature, compare, for example, the article Poromeric Man-Made Upper Materials in the journal Leather of Sept. 8, 1967, pp. 389-390, the article Poromeric Heel Dragging in the journal Chemical Week of July 26, 1969, 'pp. 43-44, the article by Dr. W. Roddy in the journal The Leather Manufacturer of May 1967, pp. 63-66, and the article in the journal Chemie-fasern," 1967, No. 1, pp. 730-734. The poromerics may consist of the most diverse artificial or natural materials, for example, linear polyesters, polyacrylonitrile, synthetic polyamides and polyurethanes; they must, however, possess the typical poromeric structure. This structure can, for example, be characterized in that the materials must possess a water vapor permeability of at least 0.5 milligram/ cm. per hour, that the pores, however, must be micropores, which do not allow water to pass through directly and that, finally, the materials must resemble leather in appearance.

Before printing in accordance with the process of the present invention, the leathers may advantageously be Patented Feb. 26, 1974 treated with a suitable primer or dressing agent, for example with one based on an acrylate resin or a polyurethane, so as to improve the adhesion, scratch resistance, crease resistance and abrasion resistance.

The temporary carriers to be used according to the process comprise, as the base layer, an optionally laminated aluminium foil, or a sheet or a strip of regenerated cellulose or paper, preferably a paper with few pores, or none at all for example Kraft paper. The sheets are coated with a mixture of nitrocellulose and an aminoplast. The proportion of nitrocellulose in this mixture is preferably within the range of from 40 to A urea-formaldehyde condensate is preferably used as the aminoplast. The best results are obtained with alcoholsoluble condensates.

The thickness of the transferable film of vinyl resins is preferably from 0.5 to 10 Polyvinyl chloride or a copolymer of vinyl chloride and vinyl acetate, consisting for example of to of vinyl chloride and 20 to 15% of vinyl acetate, are appropriatelyused as vinyl resins. The transferable film can consist of one or more layers; for example, it may consist of a layer of an unpigmented vinyl resin and overlying layers of pigmented vinyl resins. The pigmented layer or layers lying overlying the unpigmented vinyl resin layer may also comprise a different resin, for example an acrylic resin. The pigment particles are appropriately encapsulated by the vinyl resin.

Inorganic pigments, for example, carbon black, metal powders, titanium dioxide, hydrated iron oxides, ultramarine and chromium oxide may be used as pigments, but organic pigments, for example from the class of the azo, anthraquinone, phthalocyanine, nitro, perinone, perylenetetracarboxylic acid diimide, dioxazine, thioindigo or quinacridone dyestuffs, may especially be used.

The temporary carrier is appropriately manufactured in accordance with the instructions of Swiss patent application No. 14,585/69, by printing one of the surfaces of the paper base layer with a solution or emulsion of nitrocellulose and aminoplast in a volatile organic solvent, and thereafter drying the material. A thin layer is thus obtained which contains a mixture of aminoplast and nitrocellulose. The paper should contain from 1 to 20 g. of this mixture per mi.

The base layer prepared in this way can be printed directly with a printing ink containing the vinyl resin and a finely divided pigment, which is advantageously encap sulated by a vinyl resin. It has, however, proved advantageous to print the substrate first with an unpigmented vinyl resin layer and then with one or more pigmented vinyl resin layers or with a pigmented resin of some other composition, for example with an acrylic resin. Multicolor designs can be obtained if printing rollers inked in difierent colors are used.

The transfer of the transferable film from the temporary mrrier to the ultimate carrier is preferably effected by pressing them together at an elevated temperature, advantageously at a temperature within the range of from 80 Q to C. The carrier paper can thereafter be stripped off easily.

The prints obtained are generally distinguished by excellent adhesion, crease resistance and scratch resistance. It is advantageous to provide the printed leather surface with a transparent protective lacquer.

The following Examples illustrate the invention. Unless otherwise stated, the parts denote parts by weight, and the percentages denote percentages by weight.

of ethyl acrylate and butyl acrylate, using approximately 5 g. of solids per m.

After drying in air, a transfer paper, the manufacture of which is described below, is pressed onto the leather at 100 C. for seconds and under a pressure of 70 kg./cm. and the carrier paper is stripped off. A printed pattern of good adhesion, crease resistance and scratch resistance is obtained.

Manufacture of the transfer paper One surface of a kraft paper is printed successively with the lacquers of the following composition: Lacquer No. l:

21 parts of a urea-formaldehyde resin (registered trade name Plastopal AT) 20 parts of nitrocellulose, containing 11.4% of N 2 parts of octyl phthalate parts of isopropyl alcohol 47 parts of methyl ethyl ketone Lacquer No. 2:

parts of a copolymer of 85% of vinyl chloride and 15% of vinyl acetate (molecular weight approximately 9,000)

85 parts of methyl ethyl ketone.

Lacquer No. 1 (viscosity 30 seconds in a 4 mm. Ford cup) is printed by the gravure process, using a screen engraving of 45 lines per cm., and lacquer No. 2 (viscosity seconds in a 4 mm. Ford cup) is printed with a screen of 60 lines per cm.

After drying, colored designs are printed onto the surface which has been treated in this way, using printing rollers inked in different colors, the printing inks having the following composition:

12% of a pigment preparation, comprising 50% of a pigment and of 50% of a copolymer of 85% of vinyl chloride and 50% of vinyl acetate (molecular weight 9,000), 6% of a copolymer of 85% of vinyl chloride and 15 of vinyl acetate (molecular weight 9,000), 10% of toluene and 72% of methyl ethyl ketone.

After drying, the paper is ready .for transfer printing.

EXAMPLE 2 Semi-chrome-tanned and dyed sheepskin leather for garments is pressed together with a transfer paper, the manufacture of which is described in the preceding Example, and the combination is simultaneously heated to a temperature of 130 C. for 10 seconds. After removing the carrier paper, a printed pattern of very good crease resistance and scratch resistance is obtained.

EXAMPLE 3 Flulfed split leather is primed by a method known per se and coated with an aqueous binder suspension, pigmented white (coating weight approximately 50 g. of solids/m3). After drying, it is pressed together with a transfer paper, the manufacture of which is described in 'Example 1, and the combination is simultaneously heated to 110 C. for 5 seconds. After removing the carrier paper, the leather is overlacquered with a clear lacquer based on a mixture of a methylmethacrylate resin and a vinyl chloride-vinyl acetate copolymer resin. The printed leather thus obtained is distinguished by high adhesion and crease resistance of the print and by high light resistance.

What is claimed is:

1. A process for printing natural or synthetic leather wherein the improvement consists essentially of (a) contacting the surface of the leather to be printed with a temporary carrier of paper, aluminum or regenerated cellulose, said temporary carrier comprising a transferable film of vinyl resin and one or more pigments, and an underlying layer of a mixture of nitrocellulose and an aminoplast and (b) separating the temporary carrier from the surface of the leather which retains the transferable film.

2. A process as claimed in claim 1, wherein the transferable film contains 1 to of a finely divided pigment.

3. A process as claimed in claim 1, wherein the transferable film comprises a layer of an unpigmented polyvinyl chloride and an overlying layer of a pigmented polyvinyl chloride or copolymer of vinyl chloride and vinyl acetate.

4. A process as claimed in claim 1, wherein the underlying layer comprises a mixture of nitrocellulose and a urea-formaldehyde resin.

5. A process as claimed in claim 4, wherein the ureaformaldehyde resin is soluble in alcohol.

6. A process as claimed in claim 1, wherein the surface to be treated and the temporary carrier are superimposed with the simultaneous application of at least one of heat or pressure.

7. A process as claimed in claim 6, wherein the temperature is within the range of from 80 to 150 C.

8. A process as claimed in claim 7, wherein before separating the temporary carrier from the surface of the leather, the combination is cooled.

9. A process as claimed in claim 1, wherein the temporary carrier used is an aluminum foil, the transferable film of which comprises polyvinyl chloride or a copolymer of vinyl chloride and vinyl acetate.

10. A process as claimed in claim 9, wherein the copolymer comprises 80 to of vinyl chloride and 20 to 15 of vinyl acetate.

11. A process as claimed in claim 9, wherein the thickness of the transferable film is within the range of 0.5 0 10;!

12. A process as claimed in claim 9, wherein the nitrocellulose mixture additionally contains an alkyd resin.

13. A process as claimed in claim 9, wherein the foil contains 1 to 20 g. of the nitrocellulose mixture per m.

14. A process as claimed in claim 9, wherein the underlying layer is a mixture of nitrocellulose and an aminoplast and wherein said mixture contains about 40 to 60% nitrocellulose.

References Cited UNITED STATES PATENTS 3,298,850 1/1967 Reed et a1. 1l7-3.1 3,574,049 4/1971 Sander 1173.1 X 2,029,377 2/1936 Kaplan 156-241 X 2,572,967 10/1951 Axelrod l56240 X 3,519,456 7/1970 Reed et a1. 156-240 X 3,535,183 10/1970 Marriott et a1. 1173.1 X

ALFRED L. LEAVITT, Primary Examiner C. WESTON, Assistant Examiner U.S. Cl. X.R. 

